The present invention relates to a photoresist composition and, more particularly, to a photoresist composition that includes a polymer having at least one monomer that includes an acrylate or methacrylate group and further includes at least one fluoro alcohol group.
The patterning of radiation sensitive polymeric films with high energy radiation such as photons, electrons or ion beams is the principle means of defining high resolution circuitry found in semiconductor devices. The radiation sensitive films, often referred to as photoresists regardless of the radiation source, generally consist of multicomponent formulations that are usually spin-cast onto a desired substrate such as a silicon wafer. The radiation is most commonly ultraviolet light of the wavelengths of 436, 365, 257, 248, 193 or 157 nanometers (nm), or a beam of electrons or ions, or xe2x80x98softxe2x80x99 x-ray radiation, also referred to as extreme ultraviolet (EUV) or x-rays. The radiation is exposed patternwise and induces a chemical transformation to occur that renders the solubility of the exposed regions of the films different from that of the unexposed areas when the films are treated with an appropriate developer, usually a dilute, basic aqueous solution, such as aqueous tetramethylammonium hydroxide (TMAH).
Photoresists are generally comprised of a polymeric matrix, a radiation sensitive component, a casting solvent, and other performance enhancing additives. The highest performing photoresists in terms of sensitivity to radiation and resolution capability are the group of photoresists termed xe2x80x9cchemically amplified.xe2x80x9d Chemically amplified photoresists allow for high resolution, high contrast and high sensitivity that are not afforded in other photoresists. These photoresists are based on a catalytic mechanism that allows a relatively large number of chemical events such as, for example, deprotection reactions in the case of positive photoresists or crosslinking reactions in the case of negative tone photoresists, to be brought about by the application of a relatively low dose of radiation that induces formation of the catalyst, often a strong acid. The nature of the functional groups that comprise the polymeric matrix of these photoresists dictates the tone of the photoresist (positive or negative) as well as the ultimate performance attributes.
The nature of the polymeric matrix also dictates the suitability of a given photoresist for exposure with particular radiation sources. That is, the absorbance characteristics of a polymer must be carefully considered when designing a material for lithographic applications. This is important with optical lithography where polymers are chosen to provide a relatively transparent matrix for radiation-sensitive compounds such as photoacid generators (PAGs). Absorbance characteristics are also important because the wavelength of radiation used in optical lithography is directly proportional to the ultimate resolution attainable with a photoresist. The desire for higher resolution causes a continuing drive to shorter and shorter radiation wavelengths. For example, the phenolic polymers used for 248 nm imaging, namely derivatives of poly(4-hydroxystyrene) or PHS, are unsuitable for use with 193 nm radiation as the opacity of these PHS materials at 193 nm does not allow for sufficient radiation to create an appropriate image profile throughout the photoresist film thickness. Therefore, material selection and creation is necessary for each wavelength of optical radiation used.
In addition to absorbance characteristics, another parameter to be considered in the design of new photoresist materials is the dissolution behavior of the material in the given developer. The semiconductor industry has largely supported the use of 0.263 normal (N) TMAH as a developer for photoresist. The aforementioned PHS materials used in 248 nm imaging have a distinct and beneficial31property in that these materials tend to dissolve very uniformly in 0.263 N TMAH, without swelling. Additionally, the rate at which the polymeric films dissolve can be tuned by the use of, for example, protecting groups and dissolution inhibitors in positive tone photoresists, and by effective crosslinking and other functionalization in negative tone photoresists. This property of uniform dissolution has been a difficult property to incorporate into new photoresist materials, especially those designed specifically for 193 nm imaging. The current polymer platforms chosen for 193 nm imaging, such as acrylic acid derivatives, cyclic olefins and alternating cyclic olefin-maleic anhydride-based materials, generally fall into this category of nonlinear dissolution. In fact, these materials often exhibit significant swelling during the initial stages of development. This has made the development of photoresists based on these materials quite challenging, particularly so for negative tone formulations.
Alternative materials based on fluoroalcohols have been previously proposed as a means of providing aqueous base solubility. See, e.g., H. Ito et al., xe2x80x9cPolymer Design for 157 nm Chemcially Amplified Resists,xe2x80x9d Proc. SPIE, 4345:273-284 (2001); R. R. Kunz et al., xe2x80x9cExperimental VUV Absorbance Study of Fluorine-Functionalized Polystyrenes,xe2x80x9d Proc. SPIE, 4345:285-295 (2001); and Y. C. Bae et. al., xe2x80x9cRejunvination of 248 nm Resist Backbones for 157 nm Lithography,xe2x80x9d J. Photopolym. Sci. Tech., 14:613-620 (2001). Examples of such materials include norbornene hexafluoroalcohol, styrene hexafluoroalcohol and cyclohexyldodecylfluoroalcohol-based polymers. While each of these platforms provides base-soluble materials, each has disadvantages for commercial high resolution photoresist applications. The norbornene hexafluoroalcohol monomer requires special polymerization conditions, such as ring-opening polymerization, transition metal catalyzed addition polymerization, or alternating free-radical polymerization with a comonomer such as maleic anhydride. Thus, this monomer does not accommodate a large number of suitable comonomers; a desirable property which allows for a large degree of variation in composition, and thereby, materials properties. The styrene hexafluoroalcohol-based polymers are not suitable for imaging with 193 nm radiation due to their opacity at this wavelength, as with other styrenic materials such as PHS. The cyclohexyldodecylfluoroalcohol acrylates suffer from their high degree of synthetic complexity thus rendering their manufacture prohibitively expensive.
Accordingly, a need exists for new, practical compositions that can provide the desired characteristics for high resolution photoresist applications.
In a first aspect of the invention, a photoresist composition is provided. The composition includes a polymer having at least one monomer having a formula: 
where R1 represents hydrogen (H), a linear or branched alkyl group of 1 to 20 carbons, or a semi- or perfluorinated linear or branched alkyl group of 1 to 20 carbons; and where R2 represents an unsubstituted aliphatic group, or a substituted aliphatic group having zero or one trifluoromethyl (CF3) group attached to each carbon of the substituted aliphatic group, or a substituted or unsubstituted aromatic group; and where R3 represents hydrogen (H), methyl (CH3), trifluoromethyl (CF3), difluoromethyl (CHF2), fluoromethyl (CH2F), or a semi- or perfluorinated aliphatic group; and where R4 represents trifluoromethyl (CF3), difluoromethyl (CHF2), fluoromethyl (CH2F), or a semi- or perfluorinated substituted or unsubstituted aliphatic group.
The composition can further include at least one of a solvent, photoacid generator, crosslinking agent, basic compound, surfactant, latent basic compound, photobase generator, dissolution inhibitor, dissolution accelerator, adhesion promoter, and defoaming agent. These additional materials can be included to provide desired properties. A crosslinking agent can be included, for example, in a negative tone photoresist, or an agent containing an acid labile group can be included, for example, in a positive tone photoresist.
The photoresist can also include a co-monomer that does not fall within the formula set forth above. The co-monomers can be selected based upon the properties desired in the photoresist composition. For example, certain co-monomers can provide crosslinking groups desired in a negative tone photoresist. Other co-monomers can provide properties desired in a positive photoresist. Still other co-monomers can provide properties desirable in either a positive or negative tone photoresist, such as regulation of dissolution properties, thermal properties, and etch resistance.
In another aspect of the invention, a novel composition is provided. The composition includes a polymerizable monomer selected from the group consisting of 1,1,1-trifluoro-2-trifluoromethyl-2-hydroxy-5-pentyl methacrylate; 1,1,1-trifluoro-2-trifluoromethyl-2-hydroxy-4-pentyl methacrylate; 2-{[5-(1xe2x80x2,1xe2x80x2,1xe2x80x2-trifluoro-2xe2x80x2-trifluoromethyl-2xe2x80x2-hydroxy)propyl]norbornyl]} methacrylate; or analogous acrylate monomers each thereof. A composition is also provided that includes a polymerizable monomer selected from the group consisting of 3-furfuryloxy-2-hydroxyprop-1-yl methacrylate; 6-methacryloxymethyl-2-naphthol; 2-methacryloxy-6-hydroxymethylnaphthalene; or analogous acrylate monomers each thereof.
In another aspect of the invention, a method of patterning a substrate is provided. The method includes applying a photoresist composition as described above to form a film, patternwise exposing the film to an imaging radiation source, and developing areas of the composition exposed to the radiation source. The method can further include etching the patterned substrate, for example, using ion etching.
A distinction of these acrylate and methacrylate materials over others used in lithographic photoresist formulations are the incorporation of the fluorinated alcohols as the base-solubilizing moiety. These materials can have a pKa similar to that of the aforementioned phenolic materials (pKa xcx9c9-11) and thus can exhibit similar dissolution characteristics in TMAH. This is in contrast to the acrylic acid or carboxylic acid derivatives that are often currently employed, which rely on the alkali solubility of the acid functionalities, which are significantly stronger acids (pKa xcx9c3-6) and thus have distinct dissolution characteristics.
The acrylate-based or methacrylate-based compositions of the invention provide several distinct advantages over conventional materials. Firstly, a variety of synthetic variations are easily attainable through modification of the ester functionality. Secondly, these monomers readily undergo free-radical polymerization and are amenable to free-radical copolymerization with other co-monomers. Free radical polymerization is desirable as the functional group tolerance of this means of polymerization is high and control of molecular weight and polydispersity is facile. Thirdly, polymers derived from acrylate or methacrylate monomers are generally quite soluble in conventional casting solvents and form high quality, uniform films when cast on conventional substrates.
The photoresist compositions of the invention offer the ease of synthetic variation and polymerization afforded by acrylates or methacrylates with the superior dissolution characteristics offered by fluoro alcohols. The variety of materials described in this application have been incorporated into both positive and negative tone photoresists that allow high resolution patterning with 193 nm optical radiation. Furthermore, the performance of such resists can be extended by including blends of fluoro alcohol acrylate polymers with other similar or dissimilar polymers in the resist formulation.